Heretofore, a curable composition, which is cured by actinic rays such as ultraviolet rays and electron rays, or by heat, has been utilized in practice for various applications such as paints, adhesives and printing inks on such as plastics, paper, wood and inorganic materials; printed circuit boards and electric insulation related materials. In recent years, as for printing ink, paints and adhesives among others, further improvement in weather-resistance and adhering capabilities have been sought. Further, as ink-jet ink utilizing these, ultraviolet curable ink-jet ink, which is cured by ultraviolet rays, is common. An ink-jet method utilizing this ultraviolet curable ink has attracted attention in recent years with respect to relatively low odor, rapid drying and capability of recording on non-paper recording media without an ink absorptive property, for which an ultraviolet curable ink-jet ink has been disclosed in such as Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 6-200204 and Japanese Translation of PCT International Patent Application Publication No. 2000-504778. In this field, a major requirement is to exhibit high strength of the formed film and a low viscosity of the ink.
Further, in the case of utilizing this ink, curing sensitivity is liable to vary depending on the types of recording medium and working environment. When a cationic polymerizable compound is utilized, there is no oxygen inhibition effect, however, there is a problem of great influence of water content (moisture) at the molecular level (for example, please refer to Patent Documents 1, 2 and 3).
Further, when an image is formed by use of ink utilizing a cationic polymerizable compound, liquid ink drops are ejected onto a previously cured ink layer to also be cured, in this case, it has been newly proved that the diameter of a dot is liable to be broaden, which tends to blur the image.
Heretofore, as a control technology of the dot diameter of ejected UV curable ink-jet ink, addition of a silicone type or fluorine type surfactant has been disclosed (for example, please refer to Patent Documents 4, 5 and 6), however, it has been proved that although any of these is effective as a dot diameter control means, the nozzle surface of the head becomes easily wetted by ink, resulting in a problem such as poor ink ejection behavior and generation of stains on a printed matter, particularly in the case of utilizing an ink-jet head provided with a metal nozzle.
[Patent Document 1]JP-A2002-188025[Patent Document 2]JP-A2002-317139[Patent Document 3]JP-A2005-325155[Patent Document 4]JP-A2003-147233[Patent Document 5]JP-A2004-182933[Patent Document 6]JP-A2005-120201